The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones. These more than 20 bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. They are coupled sequentially to one another by tri-joint complexes that consist of an anterior intervertebral disc and the two posterior facet joints. The anterior intervertebral discs of adjacent bones are cushioning cartilage spacers.
The spinal column of bones is highly complex in that it includes these 20 bones coupled to one another (and others), and it houses and protects critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic, congenital and/or developmental irregularities are the principle causes that can result in spinal pathologies in which the natural curvature of the spine lost. Scoliosis is a very common one of these types of irregularities, resulting in a sequential misalignment of the bones and intervertebral discs of the spine. Major causes of scoliosis are idiopathic (i.e., unknown cause), congenital developmental anomalies and neuromuscular disorders such as cerebral palsy. The misalignment usually manifests itself in an asymmetry of the vertebral bodies, such that, over a sequence of spinal bones, the spine twists and/or bends to one side. In severe cases, neurological impairment and/or physiological disability may result.
The present surgical technique for treating scoliosis (as well as other spinal conditions) includes the implantation of a plurality of hooks and/or screws into the spinal bones, connecting rods to these elements, physically bracing the bones into the desired positions, and permitting the bones to fuse across the entire assembly. This immobilization often requires anterior plates, rods and screws and posterior rods, hooks and/or screws. Alternatively, spacer elements are positioned between the sequential bones, which spacers are often designed to permit fusion of the bone into the matrix of the spacer from either end, hastening the necessary rigidity of the developing bone structure. Spacers allow bone fusion to grow into or around them. There are two classes of intervertebral spacers: horizontal cages such as the BAK™ and Ray cages, as described and set forth in exemplary U.S. Pat. Nos. 5,015,247 to Michelson and 5,026,373 to Ray et al., respectively, and vertical cages such the Harms cages, as described and set forth in exemplary U.S. Pat. No. 4,820,305.
Similar techniques have been employed in other spinal infirmities, including collapsed disc spaces (failure of the intervertebral disc), traumatic fractures, and other degenerative disorders. While the present invention has many applications, such applications include the treatment of any spinal disorder in which the space between vertebral bones needs to be surgically separated (the bones distracted), realigned and then fused to one another.
A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, and the insertion of implants and/or height restorative devices, several methods and devices have been disclosed in the prior art.
Restoring the appropriate height and orientation of the vertebral bones and the intervertebral space is the first step in the surgical strategy for correcting this condition. Once this is achieved, one class of surgical implantation procedures involves positioning a device into the intervening space. This may be done through a posterior approach, a lateral approach, or an anterior approach. Various implant devices for this purpose include femoral ring allograft, cylindrical metallic devices (i.e., cages), and metal mesh structures that may be filled with suitable bone graft materials. Some of these implant devices are only suitable for one direction of approach to the spine. All of these devices, however, are provided with the intention that the adjacent bones will, once restored to their appropriate alignment and separation, then grow together across the space and fuse together (or at least fuse into the device implanted between the bones).
Most recently, the development of non-fusion implant devices, which purport to permit continued natural movement in the tri-joint complex have provided great promise. The instrumentation and methods for the implantation of these non-fusion devices, as well as the implantation of the fusion devices catalogued previously, therefore should integrate the functions of restoring proper anatomical spacing and easy insertion of the selected device into the formed volume.
It is, therefore, an object of the present invention to provide a new and novel treatment for scoliosis, as well as for the treatment of spinal pathologies in general.
It is, correspondingly, another object of the present invention to provide an intervertebral distraction trial tool which more accurately and easily separates collapsed intervertebral spaces.
It is further an object of the present invention to provide an intervertebral distraction trial tool which more can be used to correct scoliosis and/or restore normal alignment to the spine.
It is further an object of the present invention to provide an instrument that proficiently and simply manages the insertion, rotation, and removal of the intervertebral distraction trial tools.
It is further an object of the present invention to provide an implantable spacer device that permits more anatomically appropriate and rapidly osteogenic fusion across the intervertebral space.
Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.